快猫短视频

IT MAY be gone, but the moa is not forgotten. Researchers have managed to
sequence all its mitochondrial DNA.

It鈥檚 the first time anyone has done this for an extinct animal. Not only is
the work plugging important gaps in the family tree of flightless birds, or
鈥渞atites鈥�, it is also fuelling debate on how the ancient supercontinent of
Gondwanaland broke apart (see maps).

Alan Cooper of the University of Oxford and his colleagues in Britain and
Spain extracted DNA from the fossilised bones of two moas and one elephant bird,
an extinct species from Madagascar. They managed to sequence only the very short
pieces of DNA found in the mitochondria of cells.

鈥淪equencing the nuclear genomes of extinct species is not going to be
possible,鈥� Cooper says, as the fragments are too small and damaged to be
reassembled. They also sequenced the mitochondrial genomes of living flightless
birds such as the emu, cassowary, kiwi and two species of tinamou.

The team compared all these sequences with published sequences of the rhea,
ostrich and chicken. Their analysis confirmed earlier ideas that kiwis
and moas evolved after two separate migrations of ratites into New Zealand. The
researchers also estimate that ratites first appeared in the Late Cretaceous,
over 65 million years ago.

Reconstructing these family trees also gives clues to when different species
colonised land masses. Cooper and his team used the divergence dates to evaluate
different theories as to how the ancient supercontinent of Gondwanaland broke up
into Africa, Australia, New Zealand, South America and Antarctica.

For example, did Africa split away first, or did it break away along with
South America? Ostriches clearly split from other ratites after the separation
of Africa and South America, supporting the idea that land bridges existed
between Australia/Antarctica and Indo-Madagascar, says the team.

But Paul Upchurch, a palaeobiogeographer at the University of Cambridge,
doubts that studying a single group of animals will give enough information to
draw conclusions about the break-up of Gondwanaland, especially as the ratite
fossil record is so scanty. 鈥淵ou have to appreciate that there鈥檚 a lot of
missing data,鈥� he says.

鈥淲e鈥檙e not trying to claim any new geological splits because of our data,鈥�
Cooper replies. 鈥淏ut the many species do show these routes must have existed.鈥�
That adds to the geological evidence, he says.